Nate Brune, a 16-year old high school student, just released:

dEFIant: The best UEFI game engine on the market!
The only ring0 game engine on the market
https://github.com/NateBrune/dEFIant

There are a few other UEFI games, but there are so few that I doubt “best UEFI game engine” cannot be argued with, yet. 🙂 I like the name, reminds me of “rEFIt” and “rEFInd”.

Back in 2013, Matthew Garrett ported Zork’s Z-Machine to UEFI:
http://mjg59.dreamwidth.org/27881.html

Also back in 2013, there’s a Tetris implementation for UEFI:
https://github.com/swmicro/Tetris

There’re 1-3 other UEFI games on Github, sorry no better pointers but here:
https://github.com/search?utf8=%E2%9C%93&q=UEFI&type=Repositories&ref=searchresults

Somewhere I think I still have patches for GNU Go and BSD Fortune ports, from when I was learning to use the EADK. 😦 I’m waiting for someone to port MAME to UEFI, only then will UEFI be “the new DOS”. 🙂